Not applicable
This invention relates to image projectors and, more particularly, to image edge blending techniques for use in projection systems employing multiple image projectors to form a perceptually seamless overlapping, composite image.
Prior projection systems have employed two or more projectors to form a composite image. In a two projector system, the projected images are positioned side-by-side or one on top of the other. Projector systems can also include an array of projectors. When two projectors are employed, one projector projects a first portion of an image, and a second projector projects a second portion of the image. The first and second projectors are positioned such that the first and second images are projected adjacent to each other onto a screen. Skilled workers will appreciate that it is difficult to precisely align the two or more projectors such that the seams between the first and second images are perceptually invisible to the viewer.
To improve the appearance and perceptual continuity of projected composite images, the first and second projectors are positioned such that the first image slightly overlaps the second image to a form a seamless composite image. When the projectors are partially overlapped, the overlap region contains the illumination level for both projectors, and the overlap region has a greater image intensity because the brightness levels are added together. Accordingly, a bright stripe is produced in the overlap region.
To alleviate this problem, conventional light valve projection systems have employed brightness adjustment electronics to eliminate the excessive brightness in the image overlap region. These electronic smoothing devices can not, however, correct for off-state illumination levels in the image overlap region without significantly reducing image contrast. The off-state, or black level, of many light-valve-based projectors still contain some illumination. Therefore, the overlap region contains the off-state illumination level of both projectors.
The black, or off-state illumination level, is the lowest light level that can be achieved by a light valve projector. It is not, therefore, possible to lower this off-state level further by electronic signal correction. Alternatively, electronic signal correction can be employed to raise the black level of the non-overlapping regions to a level equal to the illumination level in the overlapping region. However, this electronic correction is not desirable because it significantly reduces the overall contrast ratio of the light valve projection system and cannot be used for applications such as night simulation where high contrast is required.
To solve these problems other prior workers have extensively modified the internal optical engines of light-valve-based image projectors to include image edge blending devices that cause controlled edge illumination gradation without sacrificing contrast. For example, U.S. Pat. No. 6,017,123 for PROJECTED IMAGE BLENDING FOR MULTIPLE IMAGES describes placing blending devices, such as filters and/or solid masks, at various positions along the light path of a light-valve-based projection system including a light source, light valve, combiner, projection lens, and screen. Embodiments are described in which the blending device is placed internal to the projector at or near and image plane associated with the light source, light valve, or combiner. In other embodiments the blending device is placed external to the projector between the projection lens and the screen.
All of these embodiments have associated problems. The embodiments external to the projector are difficult to adjust. Some of the embodiments internal to the projector require three blending devices if implemented in a three-path color projector. Placing blending devices in the light source path requires the undue expense of improving the light source optics to properly image the blended edge on the light valve. All of the internal embodiments require either extensively modifying existing projectors or building them originally to include blending devices. Such internal embodiments further preclude adapting existing blending devices to a wide variety of projectors.
What is still needed, therefore, is a simplified method and apparatus for blending illumination levels of overlapping image portions formed by a multiple conventional projector image projection system to form perceptually seamless composite images having maximum contrast.
An object of this invention is, therefore, to provide an apparatus and a method for adapting an image edge blending assembly to a conventional image projector.
Another object of this invention is to provide an image edge blending apparatus and method that is adaptable to a wide variety of projector types, models, and projection lenses.
Yet another object of this invention is to provide an image edge blending apparatus and method that requires only a single edge blender for use with three-path color projectors.
A further object of this invention is to provide an image edge blending apparatus and method that minimizes the casting of stray light outside projected image margins.
An image edge blender assembly of this invention installs in an unmodified projector in place of the projection lens. The projection lens is then installed at the output end of the image edge blender assembly. The image edge blender assembly includes a relay lens assembly that relays an objective image plane formed in the projector to an intermediate focal plane formed within the image edge blender assembly.
The lens mount of the image edge blender assembly is compatible with the lens mount of the projector. Furthermore, the image edge blender assembly includes a second lens mount for receiving the projection lens. Accordingly, by retooling the lens mounts, the image edge blender assembly can be adapted for use with a wide variety of projectors and projection lenses.
Positioned at or near the intermediate focal plane is an adjustable aperture assembly that includes at least one shutter movable in rotational, parallel, and transverse directions relative to the optical axis. Each shutter includes an aperture edge that is preferably opaque and sharp. The open area surrounding the optical axis as bounded by the aperture edge or edges forms the adjustable aperture of this invention. The aperture is adjustable in parallel distance from the intermediate focal plane, rotatable about the optical axis and adjustable in transverse distance from the optical axis. The aperture edge or edges are positioned at or near the intermediate focal plane to produce the desired image edge brightness gradient from transmissive to obscured. The resulting projected image is the original image produced by the projector, modified by the adjustable aperture such that at least one projected image edge gradually fades to black without perceptual geometric distortion or color aberrations. The modified image at the intermediate focal plane is projected by the projection lens onto a screen.
Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof, which proceeds with reference to the accompanying drawings.